Thanks. That's interesting.... There is only 1mm difference in the width of 8-speed and 9-speed cassettes. Also, if it will index with 8-speed, I'm pretty sure that means it would index with 9 speed. (Pretty sure than Shimano 9-speed shifters were compatible with 8-speed derailleurs and vice versa). Also, I measured the total throw of the derailleur at 42mm, which is more than enough for any size cassette (assuming it lines up right so there isn't much wasted travel).

The real question is probably going to be how large a cog it will shift over.... My impression is people weren't much for putting 32t cogs on road bikes back when these were made.

Ah, well, guess worst case is it doesn't work and I have to use an xt or similar derailleur. (Would rather use Sram Apex given a choice, but they never made 9-speed bar end shifters - or 8, for that matter, and I'm not sure there is a Shiftmate that works to match this derailleur to Shimano shifters).